In the foundry industry, one of the procedures used for making metal parts is by sand casting. In sand casting, disposable molds and cores are fabricated with a mixture of sand and an organic or inorganic binder. The binder is usually used to strengthen the cores, which are the most fragile part of the mold assembly.
One of the fabrication processes used in sand casting is the no-bake process. In this process a liquid curing agent is mixed with the sand and binder to cure the mixture.
A binder commonly used in the no-bake fabrication process is a polyurethane binder derived from curing a polyurethane-forming binder composition with a liquid tertiary amine catalyst. The polyurethane-forming binder composition usually consists of a phenolic resin component and polyisocyanate hardener component. Such polyurethane-forming binder compositions, used in the no-bake process, have proven satisfactory for casting such metals as iron or steel which are normally cast at temperatures exceeding about 2500 degrees Fahrenheit.
A satisfactory no-bake process which utilizes phenolic resin based polyurethane-forming binders to make foundry shapes used in casting low melting metals has not been developed. This is because the temperature of low melting metals may be as low as about 1300 degrees Fahrenheit during the casting process. This temperature is not high enough to decompose the binder in the sand. Thus, the shakeout of foundry shapes made with traditional polyurethane-forming foundry binders is too slow and/or incomplete.